Rat brain homogenates incubated with exogenous [32-P] phosphatidylcholine liberated: LYSO[32-P] phosphatidylcholine, sn-glycero-3-[32-P] phosphorylcholine, [32-P] phosphorylcholine, sn-gleycero-3-[32-P] phosphate and 32-Pi. Further investigation showed that [32-P] phosphorylcholine was released exclusively from sn-glycero-3-[32-P] phosphorylcholien by a novel diesterase activity. We propose that the enzyme be termed L-3-glycerylphosphinicocholine cholinephosphohydrolase (EC 3.1.4.-). Parallel experiments on rat liver homogenates and a P815Y mouse mastocytoma cell-lysate, revealed no diesterase activity.